1. Field of the Invention
The present invention relates to a transmission mechanism and more particularly, to a speed-change transmission mechanism for use in a laminator or the like, which allows the user to change the torque and the transmission speed.
2. Description of the Related Art
A laminator is a mall office machine commonly used to laminate a card, photo, or leaf with laminating films. When a card, photo, or leaf is covered with two laminating films and inserted into a laminator, the two laminating films with the sandwiched card, photo or leaf are delivered through two thermal-compression rolls and then well sealed. The laminated item has a nice looking, and can be kept for a long period of time.
Different laminators from different suppliers may be designed for use with different laminating films having different thickness. When laminating relatively thicker laminating films, a relatively longer heating time is required, and a relatively greater driving force is necessary to transfer the laminating films through the thermal-compression rolls. On the contrary, when transferring relatively thinner laminating films through the thermal-compression rolls, the transferring speed must be relatively accelerated, preventing deformation of the laminating films. To fit different laminating films of different thickness, a laminator must use a speed changeable transmission mechanism.
The speed control of the transmission mechanism of a conventional laminator is an electronic design. By means of switching on a control button to obtain a relatively greater current, the thermal-compression rolls of the laminator are rotated at a relatively higher speed, thereby providing a relatively higher speed ratio to have the relatively thicker laminating films with the sandwiched item be transferred through the two thermal-compression rolls. Using a relatively greater current to drive the thermal-compression rolls can overcome the resistance produced upon insertion of the thick laminating films with the sandwiched item through the gap between the two thermal-compression rolls. However, because the thermal-compression rolls are rotated at a high speed upon application of the relatively greater current, the thick laminating films with the sandwiched item are moved through the gap between the thermal-compression rolls fast, resulting in incomplete lamination of the laminating films. Further, the use of a relatively greater current causes a relatively greater thermal noise. On the contrary, when transferring laminating films with sandwiched item through the gap between the two thermal-compression rolls at a low speed, the heating time is relatively extended, however the power may be insufficient to transfer the laminating films with the sandwiched item smoothly through the gap between two thermal-compression rolls. At this time, the laminating films with the sandwiched item may be biased.
Therefore, it is preferably to use a mechanical transmission mechanism for laminator. A mechanical transmission mechanism can provide a high torque with a low transmission speed and without thermal noise when transferring relatively thicker laminating films. When transferring relatively thinner laminating films, a mechanical transmission mechanism can be operated at a low torque and high transmission speed mode.